JPH07136711A - Method for manufacturing double tube stock for manufacturing clad steel pipe - Google Patents

Abstract

PURPOSE:To manufacture a double tube stock with a specific highly accurate clearance. CONSTITUTION:An external pipe 1 and an internal pipe 2 are rolled by a plug mill and hot extrusion. Next, the inner peripheral surface of the external pipe 1 is shot blasted to remove scale. On the other hand, the inner peripheral surface and the outer peripheral surface of the internal pipe 2 are ground to remove a flaw. Next, the inner peripheral surface of the external pipe 1 and the outer peripheral surface of the internal pipe 2, are washed by thinner. Next, a double tube stock is made by fitting the internal pipe 2 in the external pipe 1. The clearance between the external pipe 1 and the internal pipe 2, is approximately 10.3mm (pipe length 5m). Next, both tip parts of the internal pipe 2, are sealed by plugs 5. While substituting nitrogen (N2) gas by a nitrogen gas cylinder 4 in the space of a joined surface part between the external pipe 1 and the internal pipe 2, a water pressure (internal pressure), for instance, 1300kg/cm<3> is applied by a high pressure plunger pump 7 via a conduit 6 let to the internal pipe 2 through the inside of the plug 5 to expand the internal pipe 2. Consequently, a double tube stock with approximately 0.4mm clearance, is manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a double element tube used for producing a clad steel tube consisting of an outer tube and an inner tube.

[0002]

2. Description of the Related Art A clad steel pipe consisting of an outer pipe made of carbon steel or the like and an inner pipe made of stainless steel, high nickel alloy steel or the like is industrially useful because of its excellent corrosion resistance and mechanical properties. It is a product. This clad steel pipe is usually manufactured by using a double element pipe consisting of an outer pipe and an inner pipe as a raw material and subjecting it to hot rolling.

As a typical example of a hot rolling method for producing a clad steel pipe from a double element pipe, a pipe manufacturing method using a Mannesmann piercing equipment (hereinafter referred to as "Mannesmann method") has been conventionally used. Since the Mannesmann method is already known technology, it will not be described in detail, but the double element pipes that are heated and diffusion bonded in a heating furnace are rolled by a punching machine shown in FIG. 4 and other drilling equipment (not shown). By carrying out the method, a clad steel pipe is manufactured. FIG. 4 is a schematic cross-sectional view showing an example of a punching machine of the Mannesmann drilling equipment, and a double element tube 3 including an outer tube 1 and an inner tube 2 is shown in FIG.
It shows a situation in which rolling is performed by the roll 11 and the piercing plug 12 of the piercing machine 9 while advancing in the direction of the arrow inside.

In the production of such a clad steel pipe,
Due to the heating of the heating furnace, the heating diffusion bonding of the double element pipe is made,
Then, by hot rolling, the outer tube and the inner tube are brought into close contact with each other with a desired bonding strength over the entire length. For this purpose, before heating, the gap between the outer tube and the inner tube (hereinafter , The distance between the inner surface of the outer tube and the outer surface of the inner tube,
It is necessary that the "clearance" has a predetermined high-accuracy dimension (for example, about 0.4 to 0.5 mm for a tube having a total length of 3 to 4 m). Therefore, the clearance at the time of fitting (assembling) the inner pipe is also required to have the above size.

As a method for manufacturing such a double element tube, a method comprising the following steps has been known in the past.

A core of a solid round bar billet for an outer pipe and an inner pipe is carved to obtain an inner pipe and an outer pipe having approximately predetermined dimensions. Alternatively, a similar steel pipe is rolled into an inner pipe and an outer pipe in the same manner.

The inner peripheral surface of the outer tube is ground smoothly by a grinder or the like, and further ground by honing (means for finishing the surface to be smooth with a grindstone). Conventionally, honing is an indispensable means for fitting the inner pipe into the outer pipe with a small clearance. On the other hand, the outer peripheral surface of the inner pipe is smoothly cut by a lathe or the like. Then, both pipes are finished so that the outer pipe and the inner pipe have a predetermined highly accurate clearance. At this time, the clearance is required to have high accuracy as described above.

Both ends of the outer pipe and the inner pipe are subjected to an excavation process for welding.

The joint surface between the inner tube and the outer tube, that is, the inner peripheral surface of the outer tube and the outer peripheral surface of the inner tube are cleaned.

The inner pipe is fitted into the outer pipe and assembled into a double pipe. At this time, since the clearance at the time of fitting is highly accurate as described above, advanced assembly technology, predetermined assembly equipment, and complicated assembly process are required.

Both ends of the assembled double pipe are seal-welded (the above is referred to as “prior art 1”).

Regarding the production of a double element pipe for producing a clad steel pipe, JP-A-59-47637 and JP-A-59-47638 disclose that the tube end portion of the inner tube is previously expanded to form an inner tube. A technique is disclosed in which the outer tube is brought into close contact with the outer tube, and then the tube is expanded by fluid pressure over the entire length to be brought into close contact (hereinafter referred to as "prior art 2").

[0013]

However, the prior art 1 has the following problems.

In the production of a raw tube from a solid round bar billet, the yield is poor because of core cutting.

Since honing is required in addition to grinding with a grinder or the like, the processing cost is high, and the work efficiency and the yield are low.

Since the inner pipe is fitted into the outer pipe having a predetermined high precision clearance, the efficiency of fitting (assembling) the inner pipe is deteriorated, and dedicated equipment is required, resulting in high assembly cost.

On the other hand, in the prior art 2, after the inner pipe is fitted into the outer pipe, both ends of the inner pipe are expanded and adhered by a method such as punching or applying a compressive load in the axial direction so that the ends of the pipes are in close contact with each other. This is a method for producing a double element tube having a uniform surface. However, in this method, the inner tube and the outer tube are not sufficiently adhered to each other in the central portion of the raw tube, and it is difficult to perform rolling with a high reduction ratio.

Therefore, an object of the present invention is to manufacture a double element pipe having a predetermined highly precise clearance by a relatively simple method, to reduce the number of element pipe processing steps, to simplify equipment cost, and to work. It is an object of the present invention to provide a method for producing a double element pipe for producing a clad steel pipe, which can achieve an improvement in efficiency and an improvement in yield.

[0019]

SUMMARY OF THE INVENTION The present invention includes an outer tube,
It is characterized in that an inner pipe having an outer diameter smaller than the inner diameter of the outer pipe is fitted into the inner pipe, and the inner pipe is expanded by water pressure so as to be in close contact with the outer pipe. Before fitting the inner tube into the outer tube, it is necessary to clean the inner peripheral surface of the outer tube and the outer peripheral surface of the inner tube.

[0020]

[Function] Since the inner pipe expands due to water pressure, a larger clearance can be taken when fitting (assembling) the inner pipe into the outer pipe. Therefore, the inner pipe is looser than the conventional one. Work becomes easy. Further, in the manufacturing process of each of the double shells, there is no need for precision grinding and honing by a grinder to obtain clearance accuracy, and as-rolled steel tubes can be used. Also,
Due to the expansion of the inner tube, the outer tube and the inner tube are in close contact with each other over the entire length of the double element tube, and a desired highly accurate clearance is obtained over the entire length of the double element tube. Furthermore, even if there is a portion with a large clearance, by removing foreign matter such as water, oil, scale, etc. by cleaning the joint surfaces (outer pipe inner peripheral surface and inner pipe outer peripheral surface), peeling does not occur without causing non-sticking parts. Does not occur.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described based on the embodiments shown in the drawings. A double element pipe for producing a clad steel pipe was prepared by the production method within the scope of the present invention shown below.

A steel pipe having the following materials and dimensions was used as each of the double raw pipes. Outer tube: Material: Carbon steel (S45C) size; Outer diameter 339.7mm x wall thickness 50.0mm x inner diameter 239.7mm (as rolled) Inner tube: Material: Stainless steel (SUS304) size; Outer diameter 219.1mm x wall thickness 12.7mm × Inner diameter 193.7 mm (as-rolled) The above steel pipe was rolled to the above dimensions by a plug mill.

Next, the inner peripheral surface of the outer pipe was shot for scale removal, while the outer peripheral surface of the inner pipe was subjected to grinder processing for the purpose of removing flaws and removing scale.

Next, the inner peripheral surface of the outer tube and the outer peripheral surface of the inner tube were washed with thinner. In this way, the joint surfaces (outer pipe inner peripheral surface and inner pipe outer peripheral surface) are cleaned, and water,
Oil, foreign matter, etc. were removed.

Next, the inner tube was fitted into the outer tube to form a double element tube. The clearance between the outer tube and the inner tube having the above dimensions was 10.3 mm (one side), and the fitting (assembling) work was easy.

Next, both ends of the inner tube 2 were sealed. As shown in FIG. 1 and FIG. 2, the sealing method is to weld the plugs 5 to both ends of the inner pipe 2 (8 is a welded portion), and to fill the joint surface space between the outer pipe 1 and the inner pipe 2 with nitrogen (N2). ) While substituting gas (4 is a nitrogen gas cylinder), water pressure is applied by a high-pressure plunger pump 7 via a conduit 6 that has passed through the plug 5 and is connected to the inner pipe 2, thus expanding the inner pipe 2. . The water pressure (internal pressure) at this time was 1300 kg / cm ³ . It should be noted that the nitrogen gas replacement is performed in order to prevent oxidation of the joint surface by air.

The double element tube thus prepared is
The dimensions of the outer tube and the inner tube were as follows. Outer tube: Size; Outer diameter 339.7 mm x wall thickness 50.0 mm x Inner diameter 239.7 mm (no change) Inner tube: Size; Outer diameter 239.3 mm x Wall thickness 12.7 mm x Inner diameter 313.7 mm Therefore, the clearance after expansion is 0.4 mm there were.

Next, both ends of the double element tube thus prepared were cut into 50 mm. The cutting of both pipe ends was carried out in consideration of the fact that the plugs were welded to both pipe ends and the inner pipe was sealed, so that the deformation of the pipe ends was restrained and the closeness became poor. The dimensions of the double element pipe after cutting are as follows. Outer tube: Size; outer diameter 339.7 mm x wall thickness 50.0 mm x inner diameter 239.7 mm Inner tube: size; outer diameter 239.3 mm x wall thickness 12.7 mm x inner diameter 313.7 mm

Next, a groove for welding was applied to both ends of the double element pipe. FIG. 3 is a partial side cross-sectional view of both ends of the double element pipe showing a groove-processed shape. As shown in FIG. 3, the depth a of the groove 10 is 20 mm, the angle with the joint surface is 65 ° (outer pipe part θ1: 45 °, inner pipe part θ2: 20 °), and the curvature of the bottom part b is R3. there were.

Then, using a stainless welding rod,
Both ends of the double element pipe were seal-welded by TIG welding.

Next, the double element tube was hot-rolled by the Mannesmann method to prepare a clad steel tube. The heating temperature in the heating furnace (BT) was 1180 ° C, and the double element pipe extracted from the heating furnace (BT) was finished as a clad steel pipe with an outer diameter of 406.4 mm × a wall thickness of 15.2 mm by the plug rolling method in the Mannesmann method. . The finished dimensions are as follows. Outer diameter 406.4 mm × wall thickness 15.2 mm (outer pipe wall thickness 12.6 mm / inner pipe wall thickness 2.6 mm)

Next, the clad steel pipe thus prepared was subjected to a peeling check by a vertical ultrasonic flaw detection test stipulated in JIS G 0601. as a result,
There were no delaminated parts in the clad steel pipe, except for the unstable parts at both pipe ends caused by hot rolling. In addition, although five identical specimens were prepared, the test results were the same for all the specimens.

In this example, the Mannesmann method was used as a method for producing a clad steel pipe from a double element pipe. The Mannesmann method is the most suitable method for the hot rolling of long and large materials, but it is produced by the method of the present invention.
The means for producing the clad steel pipe from the heavy element pipe is not limited to the Mannesmann method.

[0034]

As explained above, according to the present invention, the following industrially useful effects are brought about. By fitting the inner pipe into the outer pipe and then expanding the inner pipe by hydraulic pressure, the clearance at the time of fitting the inner pipe can be made larger than before, and the fitting (assembling) work efficiency is greatly improved. Assembling equipment can be simplified, and in the production of each elemental tube of the double elemental tube, a predetermined process such as honing processing is not required, and the unrolled steel tube can be used as an elemental tube.
Processing man-hours are reduced and yield is improved. Even if the clearance at the time of fitting and assembling is large, it is possible to obtain a double element tube having the desired high-precision clearance over the entire length of the inner and outer tube joint surfaces by expanding the inner tube, and with the same performance as before. It is possible to obtain a clad steel pipe having

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing one embodiment of an apparatus for carrying out the method of the present invention.

FIG. 2 is a schematic cross-sectional view showing an example of a tube end sealing method for a double element tube.

FIG. 3 is a side surface partial cross-sectional view of both ends of the double element pipe showing a groove-processed shape.

FIG. 4 is a schematic cross-sectional view showing a situation in which a double element pipe is rolled by the Mannesmann method.

[Explanation of symbols]

 1 Outer pipe 2 Inner pipe 3 2 Heavy element pipe 4 Nitrogen gas cylinder 5 Plug 6 Conduit 7 High pressure plunger pump 8 Welding point 9 Drilling machine 10 Groove 11 Roll 12 Drilling plug

Front page continuation (72) Inventor Motoharu Yamazaki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (2)

[Claims] 1. A clad steel pipe manufacturing method, wherein an inner pipe having an outer diameter smaller than an inner diameter of the outer pipe is fitted into the outer pipe, and the inner pipe is expanded by water pressure to be closely adhered to the outer pipe. For manufacturing dual element tubes for automobiles. 2. The method for producing a double base pipe for producing a clad steel pipe according to claim 1, wherein an inner peripheral surface of the outer pipe and an outer peripheral surface of the inner pipe are washed before the inner pipe is fitted into the outer pipe.